Blender character rigging with cloth wrapped over the body
There is a function to copy vertex groups to non-matching meshes. It is great for automatically skinning clothing on characters.

First select the character mesh, then shift + select the clothing. Press spacebar and type "transfer weights". An operator should show up. This seems to be broken in the latest blender 2.74+ but try 2.73. (I just tried on a copy of 2.71 I have laying around and it works well).

The new versions have "Transfer mesh data" but it does not seem to work for me.

Cheers!